Question

How are a triangular pyramid and a rectangular pyramid different?

Answer 1

They differ by the base.

Imagine that you drew a triangle and a rectangle on a piece of paper.

Then, pick a point above the paper, and connect all vertices of the triangle with that point. That is a triangular pyramid.

Similarly, pick a point above the rectangle, and connect each vertex of the rectangle with that point. That is a rectangular pyramid.

Answer 2

Triangular pyramid has its base as a triangle, and a Rectangular pyramid has its base as a rectangle.